1. Technical Field
The present invention relates to technology for printing images by forming dots on a printing medium.
2. Related Art
Printing devices that print images by forming dots on a printing medium enjoy widespread use as output devices for images created on a computer or images shot with a digital camera, for example. Since input tone values will outnumber the tone values of the dots that such a printing device is capable of forming, the device performs tone representation by means of a halftone process. Systematic dither processes employing dither matrices are one widely used type of halftone process. Since the content of the dither matrix has considerable influence on image quality, it has been attempted to optimize dither matrices by analytical methods such as genetic algorithms or simulated annealing using evaluation coefficients that take human visual faculty into consideration, such as disclosed in JP-A-7-177351 for example. There has also been proposed technology for improving dispersion of multiple types of dots, in printed images that are formed using multiple types of dots of different density or hue, as disclosed in JP-A-10-157167.
However, halftone processes such as the above fail to take into consideration degradation of image quality that can occur when images are printed by ejecting ink dots of several colors while scanning a common area of the printing medium (e.g. uneven color mixing of several color inks occurring in main scans).